I am planning on buying a 5.7 vortec engine with a B&m supercharger on it and I was wondering how reliable will this engine be?

 

Welcome to the board, you will find a general concensus that no stock engine read-cast pistons will tolerate any kind of forced induction in a "reliable" manner. You need to do a compression and leak down test of any engine that you are considering buying....good luck.
-Michael